[PATCH v2] IOMMU/VT-d: Fix iommu=no-igfx if the IOMMU scope contains phantom device

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

If the scope for IGD's IOMMU contains additional device that doesn't
actually exist, iommu=no-igfx would not disable that IOMMU. In this
particular case (Thinkpad x230) it included
00:02.1, but there is no such device on this platform.
Consider only existing devices for "gfx only" check.

Fixes: 2d7f191b392e ("VT-d: generalize and correct "iommu=no-igfx" handling")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
v2:
 - move existence check one level up

I have looked at existence check acpi_parse_one_drhd(), but re-using
that one wouldn't work for two reasons:
 - gfx_only logic is very much tied to acpi_parse_dev_scope()
 - pci_device_detect() in acpi_parse_one_drhd() is skipped in case of
   (implicit or explicit) iommu=force
---
 xen/drivers/passthrough/vtd/dmar.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/drivers/passthrough/vtd/dmar.c 
b/xen/drivers/passthrough/vtd/dmar.c
index 78c8bad1515a..a8c09c0c84f6 100644
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -389,7 +389,7 @@ static int __init acpi_parse_dev_scope(
                 printk(VTDPREFIX " endpoint: %pp\n",
                        &PCI_SBDF(seg, bus, path->dev, path->fn));
 
-            if ( drhd )
+            if ( drhd && pci_device_detect(seg, bus, path->dev, path->fn) )
             {
                 if ( (seg == 0) && (bus == 0) && (path->dev == 2) &&
                      (path->fn == 0) )
-- 
2.39.2